Preheat oven to 350°F

Melt the butter for the filling in an oven safe saute pan with high sides. Stir in the onion and celery. Cover the pan and cook for 7 to 8 minutes on medium heat stirring occasionally. Add the flour, stirring for 1 to 2 minutes to lightly brown it.

Whisk the chicken stock into the pan. When it starts to thicken, whisk in the milk. Add the sage, thyme, chicken and vegetables, continuing to stir until the mixture is heated through, about 5-7 minutes. Add salt and pepper to taste. Remove from heat.

Make the biscuit topping by combining the flour, baking powder, sugar, and salt in a mixing bowl. Add the butter and use your fingertips to rub it into the dry ingredients. Add the milk and stir briskly, just until the dough pulls together.

Flour your work surface and turn the dough on to it. Using floured hands, need the dough 2 or 3 times, then flatten it to 1 half inch thick. Using a small round cutter, cut the Dough into biscuits and place as many as will fit, barely touching, on top of the filling.

Bake till biscuits are golden brown and filling is bubbly, about 20 to 30 minutes, then let cool for 5 to 10 minutes before serving. Make 6 to 8 servings.